Classification of phosphate ore



Oct. 6, 1953 l. M. LE BARON 2,654,477

CLASSIFICATION OF PHOSPHATE ORE Filed Dec. 5l, 1948 2 Sheets-Sheet l Was/)er Z IN V EN TOR.

Oct. 6, 1953 M LE BARON 2,654,477

CLASSIFICATION OF' PHOSPHATE ORE Filed Deo. 31, 1948 2 Sheets-Sheet 2 [RA M. ARQN IN VEN TOR.

Patented Oct. 6, 1953 2,654,477- y CLASSIFICATION or rnosrm're oRE Ira M. Le Baron, Lakeland, Fla., asslgnor to Intel"- national Minerals & Chemical Corporation, a

.corporation of New York Application December 31, 1948, Serial No. 68,681

3 Claims. l

This invention relates generally to a process for the classification of minerals and has particular reference to the classification of phosphate ore.

The use of rollers for separating materials is not new. Rollers have been previously used. to classify beans, seeds, and the like. With certain modifications of previously disclosed principles, rollers may be used for classifying and sizing such materials as coal or metal castings. However, insofar as known, the use 'of rollers in mining processes has been confined to the removal of solid materials from other solid materials: usually to the removalof a single impurity and the recovery of a single product. Examples of such use are found in the separation of coal from shale or the separation of mica from gangue. It is to be noted that'in these processes the feed material, due to the crystalline characteristics of the material, effects, by roller separation, a segregation of one type of crystal or crystalline agglomerate from another type of crystal or crystalline agglomerate. 1n the instant novel process, however, roller separation may now successfully segregate amorphous bodies from solid ore particles with the attendant advantages hereinafter set forth.

Numerous processes have been devised for the classification of phosphate ore. The type of process used may depend upon a variety of factors such as the type of matrix in which the phosphate ore appears, the shapeand size of the phosphate ore, the initial grade of matrix, and the grade of finished product desired. The matrix, including the size and shape, of the phosphate values, varies greatly with the locality of the deposits. For example, Florida hard rock phosphate is said to occur in irregular fragmentary boulders and gravel imbedded in a matrix of clay, sand, and soft phosphate rock. Florida pebblev phosphate is likewise imbedded in a matrix .of clay and vsand and, in some deposits, contains also soft phosphate rock. At the present time pebble phosphate is the primary source of the high grade product. The BPL (Bone Phosphate of Lime) content of the beneciated product is sometimes over rI weight percent.

Tennessee deposits were originally of two principal kinds. a high grade plate rock now largely exhausted and Tennessee brown rock which is virtually 'the only type being mined in that area at the present time. Tennessee brown rock is said to be the result of leached outcrops of phosphatic limestone. The rock is generally of pebble size but tabular in shape. Its matrix is'predominantly clay with some naturally comminuted brown rock. The matrix has a BPL content of between about 45 and about 50 weight percent, and when the tabular shaped rock has been mined it has heretofore been processed to yield a product from about 50 to about 57 weight percent BPL content.

In the processing of Tennessee brown rock, preliminary washing and screening operations serve to classifythe phosphate ore into a coarse material containing the tabular shaped brown rock and an undersized material, which on being further subjected to washing, classification, and dry- -ing processes, results in a finished product of between about 50 and about 57 weight percent BPL.

However, after the preliminary washing and screening operations previously referred to,'the coarse material is found to contain, in addition to the tabular phosphate rock, relatively large clay agglomerates substantially spherical in shape, chert, and other irregularly shaped non-tabular material. In processes presently employed this coarse material is further classified by passing the material on to an endless 'belt conveyor and picking out by hand the clay agglomeraties and other irregularly shaped non-phosphatic material. The disadvantages ofhand picking are numerous and well known. For example, volume of production is limited by human capacity to pick out the undesirable constituents, and the quality of the product is more likely to vary and is generally lower than the product produced by the present invention.

It is a principal object of the present invention to separate tabular shaped components of phosphate ore from irregularly shaped components.

It is a further object of the present invention to more efliciently separate tabular shaped phosphate rock from clay agglomerates, chert, and other irregularly shaped non-phosphatic material It is still a further object of the present invention to provide for an economical, improved, and efficient process for the preliminary separation of desired phosphatic values from undesirable non-phosphatic values.

Other objects will become apparent vupon a further understanding of the invention as hereinafter more fully described.

In the present invention, the phosphate ore is subjected to washing and screening, and the coarse material containing the tabular phosphate rock, clay agglomerates, and other irregularly and angularly shaped material is subjected to the space between one or more pairs of rollers. One

roller of the pair is revolved clockwise and the other counterclockwise. The rotation of these rollers is such that the opposed surfaces move upwardly from the opening between them. The effect of the revolvingrollers on the material is generally that of agitation instead of crushing. If the surfaces of the rollers are placed the proper distance apart, only the tabular shaped phosphate rock and the insignicant amount of non-phosphatic bearing material pass between the rollers. The spacing between any pair of rollers is variable but is maintained intermediate the mean thickness of the gangue and the tabular phosphate ore.

For a more complete understanding of `this invention, reference is made to Figure 1 which is a flow sheet of the process; Figure 2, a top perspective view of the roll classifier; and Figure 3, a cross section of the roller classifier.

The phosphate matrix I, as mined, is washed using a log washer 2, or similar apparatus to deslme the same. The washed material is passed on to a stationary screen 4, with the undersized material I3, going to the ne washing sectionl I4, for further classication, drying, and eventual storage.

The oversized material 5, is again washed at 6, and in the overflow more slimes are removed. Final screening of the oversized material is accomplished pieferably in a trommel screen, 1.

The undersized material 8, is combined with the undersized material I3, obtained from the initial screening process and the total undersized material is subjected to the fine washing section I4. The product obtained here, after drying, has a BPL content of between about 50 and about 57 percent by weight.

'I'he oversized material 9, contains, in addition to the tabular phosphate ore, substantially spherical clay agglomerates which have been built up during the washing process, chert, and other irregularly and angularly shaped material. This oversized material is subjected to the action of a roll classifier I0, the details of which are shown in Figures 2 and 3, and which will subsequently be described in more detail. The oversized material II, is deposited as waste, and the undersized material I2, is subjected to grinding and storage as the finished product.

For a more complete understanding of the roll classifier, reference is made to Figures 2 and 3. The rollers, I5 and I6, are placed ordinarily with their surfaces between about 1 inch and about 1/2 inch apart. The distance between the paired surfaces is variable and will depend on the thickness of the tabular shaped rock desired to be separated. It is to be noted, however, that the distance between the rollers will always be intermediate the mean thickness of the clay agglomerates and the tabular shaped phosphate ore. As shown in Figures 2 and 3, these rollers are revolved in the manner previously described, one in a clockwise direction and the other in a counterclockwise direction upward from the material to be classified. The effect on the material is one of agitation and not crushing. The speed of rotation of the, rollers is generally between about 100 and about 150 revolutions per minute, preferably about 120 revolutions per minute. The stated speeds of rotation have been found generally to be suilcient to cause the tabular rock to drop betewen the rollers thus separating the same from the undesirable nonphosphatic components. The speed to be employed likewise depends on the grade and quantity of feed material being processed. It has been found that during the agitation of this material between the rollers, in addition to the tabular phosphate rock, noted as undersized at I2 falling between the rollers,' the larger clay agglomerates, noted as oversized material at I3. have a tendency to cause the irregularly shaped material to adhere to them. 'I'his prevents most of the smaller chert and other undesirable components from falling between the rollers along with the tabular shaped phosphate rack even though their size is such that otherwise they would pass between the pairs of rollers. Because of its inherent shape. the tabular shaped phosphate rock does not adhere to the clay agglomerates to any marked degree.

In practicing this invention, the longitudinal axes of the rollers are inclined downward from the feed source I1. This allows the undesirable clay agglomerates, chert, and other irregularly and angularly shaped material to flow down the surface of the rollers and off the discharge end 2 I, to waste while the tabular shaped phosphate rock passes between the rollers and is collected and sent to drying and grinding.

In a modication of this process, the surfaces I8, of the rollers I5 and I6, may be rendered uneven by means of rods (not shown) welded or xed by other means to the surfaces of the rollers substantially parallel to the roller axes; or, the rods may be afiixed to the surfaces of the rollers in a spiral fashion, the spiral being formed either by a single rod or by shorter sections of rod. These rods serve to increase the agitation eiect on the materia1 between the rollers when the same are revolved, and if the rod is afilxed in a spiral fashion, the gangue is aided in its movement toward the discharge end of the rollers.

Another modification of this invention consists in placing one of two pairs of rollers above the other pair. The opposed surfaces of the top pair if rollers may be set closer together than the surfaces of the lower pair, or may be otherwise varied, and the longitudinal axes inclined downward from the original source of feed. The coarse material containing tabular shaped rock. clay agglomerates, chert, and other irregularly and angularly shaped material is fed between the top pair of rollers. The tabular shaped material falling between the rollers is collected, and the thicker tabular shaped material, along with the clay agglomerates and other irregularly and angularly shaped material, .is allowed to flow down the surfaces of the top inclined rollers, falling off the end of same down between the lower pair of rollers which are inclined downward from this secondary source of feed. The larger tabular shaped material then falls between the rollers of this lower pair and the undesirable material flowing downward but iot through the rollers is led away to waste. By this means a. classification into coarse and fine tabular material is made. It is to be observed that the same principle of this modiiication may be employed using any desired number of pairs of rollers.

In still another modification of this invention, the speed of one roller of the pair may be varied with reference to the other roller of the same pair. The eiect of this is to increase the agitation of the material between the rollers.

The most desirable dimensions for the rollers has been found to be between about 10 feet and about 16 feet long and between about 10 inches and about 12 inches in diameter. The rollers may be housed in sheet steel siding I9, with the sides extending above the surfaces of the rollers. Steel plate 20, running the entire length of the rollers may then be inclined over each of the rollers but not over thespace between the rollers, providing thereby a wider area or trough into which the material may be fed, as well as preventing the feed material from being thrown permanently off the rollers. l'

Starting with an ore of between about 47' and 50 percent BPL and using the rollers heretofore described, a product of between about 55 and about 60 percent BPL is obtained. By use, on the other hand, ofthe hand picking process, a product of only between 50 and 55 percent is Iobtained from the same ore. Likewise by the use of the invention,l it has been found that between about 6 and about 9'tons per hour of feed material may be processed. Whereas, by the hand picking process, only between about 4 and about 7 tons per hour of feed material may be processed from the same ore. Thus, by the present invention, a larger quantity of higher grade phosphate material is produced. Also, the capacity of the roll classifier is greater than hand picking from an endless belt conveyor.

' mediate the mean thickness of the non-tabular material and the tabular shaped phosphatic material and moving upwardly, revolving said frollers, agitating the material between said revolving rollers and collecting therefrom a tabular phosphate material falling between the revolving rollers separate from non-tabular material.

2. In the process of classifying phosphate ore comprising essentially tabular phosphate rock,

clay and chert, wherein said ore is preliminary water-washed, and followed by a screening and sizing process in which the clay andfcliert is partially removed from the oversized-material, the improvements comprising subjecting the oversized material comprisingessentially tabular phosphate rock, clay agglomerates and chert to at least one pair of rollers, vsaid rollers having their opposed surfacespositioned intermediate the mean thickness' of the clay agglomerates' and the tabular shaped phosphatic materia1,' revolving one roller of each pair in a clockwise direction and thel other roller of eachpair in a counterclockwise direction, each rollers opposed surfaces moving upwardly, each pair of rollersinclined downward from the source of feed, agitating the material between the rollers and collecting therefrom a tabular phosphate material falling between the revolving' rollersseparatev from the clay agglomerates, chert and other non-tabular material.

3. In the process of classifying phosphate ore comprising essentially-tabular phosphate rock, clay and chert, wherein said ore is preliminarily water-washed, and followed by ascreening and sizing process in which the clay and chert is partially removed from the oversized material, the improvements comprising subjecting the oversized material comprising essentially tabular phosphate rock,vclay agglomerates and chert to at least one pair of rollers placed with their longitudinal axis parallel` and opposed surfaces positioned vintermediate .the mean ,thickness of the clay agglomerates and the tabular shaped phosphatic material, said distance being variable, inclining the longitudinal axis downward from the horizontal plane and from the source of feed, revolving one roller-cfa pair in a clockwise direction and the other-roller of the same pair in a counterclockwise' direction, the opposed surfaces of both rollers moving upwardly, thus agitating said oversized material and collecting the tabular shaped phosphate rock falling between the rollers separate from the, gangue flowing downward but failing to pass between the rollers.

r f IRA M. LE BARON.

Reference: cited in the me of this patent STATES PATENTS Number `Name Date 161,744:y Broadbent Apr. 6, 1875 1,319,665

aussen Dec. 21, 191.9 OTHER REFERENCES; 

